Networking - The OSI Seven-Layer Model - The Session Layer

The purpose of the Session layer is to establish, manage, and terminate ongoing dialogs between applications. It provides a way for applications to organize their conversations into distinct sessions rather than a single stream of bytes.

The Session layer is responsible for:

• Establishing and tearing down communication sessions between presentation entities,
• Coordinating who may transmit at any given time, and
• Recovering from interruptions by resynchronizing the dialog.

Session layer functions are usually implemented in software libraries and protocols rather than dedicated devices. Gateways and application proxies sometimes perform limited Session layer functions when relaying higher layer traffic.

The Session layer is responsible for several processes, each of which is responsible for a series of methods:

1. Session Establishment and Termination
   • Negotiating parameters for a conversation,
   • Granting and releasing permission to send data, and
   • Orderly session shutdown.
2. Dialog Control
   • Half duplex dialogs (only one side may transmit at a time),
   • Full duplex dialogs (both sides may transmit simultaneously), and
   • Token management for turn taking when several parties share a session.
3. Synchronization
   • Placing checkpoints in a data stream so that communication can resume from a known point, and
   • Allowing long transfers to be subdivided into units that can be confirmed independently.

Let us move on to layer 6, the Introduction

Copyright 1999, Marc Elliot Hall, DBA Sensation! Services